Method and apparatus for treating a board-like material with a gaseous agent

ABSTRACT

The present invention provides a method of treating board-like material with a gaseous treatment agent and an apparatus for implementing the method. According to the method, a gaseous treatment agent is passed through the board-like material being treated. The board-like material is introduced into at least one treatment zone, where the gaseous treatment agent is contacted with at least one side of the board-like material and is caused to pass through the thickness of the material. The properties of the gaseous treatment agent, including its temperature, moisture content and/or composition, are controlled as needed in order to achieve a desired effect on the board-like material being treated. The apparatus includes a chamber and a support for the board-like material in the chamber. When positioned in the chamber, the board-like material forms at least part of a partition separating the chamber into two regions. The gaseous treatment agent is introduced through nozzles into the first region, where it contacts one side of the board-like material. The other side of the board-like material is subjected to a vacuum created in the second region of the chamber. The pressure differential between the two regions of the chamber causes the gaseous treatment agent to pass through the thickness of the board-like material.

This application is the national phase under 35 U.S.C. § 371 of PCTInternational Application No. PCT/FI98/00375 which has an Internationalfiling date of Apr. 30, 1998, which designated the United States ofAmerica.

The present invention relates to a method according to the preamble ofclaim 1. The invention further concerns an apparatus according to claim11.

In the manufacture of planar materials such as wood-based boards, it isnecessary to cool the boards exiting from the press, prior to theirfurther processing. Today, the cooling is performed in a boardturner/cooler also called a cooling wheel, which is a massive rotaryunit having a diameter of 7 m typical comprised of radial slots intowhich the cut boards are inserted. In the turner, each board can coolfreely from both sides during one revolution of the turner, forinstance. The capacity of cooling turners is often a bottleneck limitingthe production speed or board length in continuously operating boardmanufacturing lines. The cooling capacity of conventional coolers cannotbe varied during operation. Also the emission of obnoxious VOC gases,that is volatile organic carbon compounds has been freely admitted tothe ambient air.

It is an object of the present invention to provide a novel method andapparatus capable of overcoming the disadvantages of prior-arttechniques.

More specifically, the invention is characterized by what is stated inthe appended claims.

The arrangement according to the invention has a number of significantbenefits. Particularly, the cooling time of the board material beingprocessed can be shortened essentially. The properties of the board mayalso be affected during the treatment process. The cooling process ofthe board can be controlled more accurately and the obnoxious VOCemissions can be confined into a closed space. Moreover, the method maybe applied prior to the cutting of the board blank into separate boardproducts.

In the following, the invention will be examined in more detail with thehelp of an example by making reference to the attached drawings in which

FIG. 1 shows schematically a simplified cooler arrangement according tothe invention;

FIG. 2 shows-an apparatus according to the invention in a partiallysectioned end view illustrating the travel of board material therein;and

FIG. 3 shows an apparatus according to the invention in a side viewpartially sectioned along line III—III of FIG. 2.

The method is suited for treating a board-like material with a gaseousagent, whereby the method is implemented as illustrated in the drawingsby passing a gaseous agent through the material 1 being treated. Themethod is based on the concept that the board material 1 being treatedis taken into at least one treatment zone 2, where the gaseous treatmentagent is contacted with at least one wall of the board and caused topass through the thickness of the board material 1 and that, ifrequired, the state of the gaseous treatment agent including itstemperature, moisture content and/or composition is/are controlled inorder to achieve a desired effect on the material 1 being treated.

In the method, the material 1 being treated is moved through at leastone treatment zone 2. The material being treated is moved continuouslyor cyclically through at least one treatment zone.

In FIG. 1 is shown diagrammatically an arrangement suitable forimplementing the method. Therein the board-like material 1 such as apressed wood-based particle board blank is moved by means of agas-transmissive conveyor 5 to a treatment zone 2. The treatment zone 2is divided into two compartments 3, 4 separated by the board material 1to be treated. To the first compartment 3 of the treatment zone (in thediagram located principally above the board material), the gaseous agentis introduced via at least one nozzle 6, wherefrom at least a portion ofthe gas is directed to pass through the board material 1 into the secondcompartment 4 of the treatment zone that is situated on the oppositeside of the board material. The passage of the gaseous agent from firstcompartment through the board material to the opposed second compartmentis chiefly attributable to the pressure difference which is providedbetween the separate compartments formed on the opposite sides of theboard material. In the arrangement shown in the diagrams, the pressuredifference is achieved by forming a vacuum to the underside of the boardmaterial with the help of at least one suction pump means 9 such as arotary vacuum pump. The opposite side of the board material is providedwith means 6, 7 for introducing the gaseous agent into the firstcompartment 3 of the treatment zone. Preferably, the first compartmentof the treatment zone is also equipped with means 10 for discharging aportion, typically the excess portion, of the gaseous agent away fromthe treatment zone. By altering the state of the gaseous treatment agentincluding its composition, temperature, moisture content and thepressure difference between the treatment zone compartments surroundingthe two sides of the board material, it is possible to exert a desiredtreatment effect on the board material. In the arrangement of FIG. 1,the gas inlet nozzle 6 is provided with a nozzle 11 serving, e.g., tointroduce steam into the flow of the gaseous treatment agent.

The second compartment of the treatment zone is provided with means 8, 9for discharging the gaseous treatment agent from the second compartmentof the treatment zone. The discharged gas can be recycled back to thetreatment process according to the invention, or alternatively, passedto postprocessing such as gas scrubbing or incineration.

All gas-transmissive board-like materials are suited for treatment inthe method according to the invention. Obviously, the treatment processparameters such as the required pressure difference are affected by thequalities of the board material to be treated and the desired treatmenteffect. Typical board materials to be treated include different kinds ofwood-based particle boards such as MDF boards, flake boards, fiberboards, OSB boards and others. For certain board materials, the requiredpressure difference may be in the order of 20 kPA when the boardthickness is, e.g., 30 mm. Then, the volumetric gas flow through theboard is about 0.1 m³/s, while for a 4 mm board the gas flow is about0.4 m³/s.

An advantageous implementation of the method according to the inventionis to affect the temperature of the board material via the treatmentaccording to the method. Principally, this goal is achieved by coolingthe board material by directing onto the board material a gas flow oflower temperature than that of the board material. The cooling processcan be complemented with other treatment effects through varying themoisture content of the treatment gas, for instance. In this manner, theproperties of the board material such as its VOC content, moisture andtemperature can be affected, or alternatively, it is possible tointroduce chemicals into the board, for instance. The cooling effect canbe controlled by altering the temperature and moisture content of thetreatment gas.

Furthermore, it is possible to use a plurality of the treatment zones 2,arranged in series and/or parallel, whereby each treatment zone can beused separately for affecting the properties of the board material viaindividually adjusted treatment gas compositions, temperature, moisturecontent or other parameters and/or pressure differences and volumetricflow rates. In an arrangement comprising a plurality of treatment zones,it is advantageous to pass the gaseous agent in at least one treatmentzone through the material being treated so that the pass-through flowdirection is essentially opposite to that used in the adjacent zone.

In a preferred embodiment, at least a portion of the gas used in thepreceding treatment zones is passed on to the next treatment zone, andso forth. For instance, one practical arrangement of the zones is suchthat the treatment gas is first introduced into the last zone of thecooling line and therefrom successively through the zones countercurrentto the board travel direction until reaching the first zone of thecooling line, whereby an optimally graded cooling effect on the board isattained.

In a preferred embodiment, the heat of the treatment gas is recoveredafter the gas has been passed through the board material. The heatrecovery may be implemented using, e.g., a heat exchanger placed on apipe 8 shown in FIG. 1, or alternatively, in a chamber 4, for instance.The recovered heat can be utilized in a conventional manner, e.g., forthe heating of a building.

Advantageously, the treatment zone is complemented with sensor devicessuch as pressure sensors 13, temperature sensors 12, moisture contentsensors 14 and/or flow rate sensors 15, whose output signals areutilized in the control of the treatment process. In the arrangement ofFIG. 1, the temperature sensors are placed into the treatment zone atthe entry end and the exit end of the board material into and away fromtreatment zone, respectively, whereby it is possible to monitor, e.g.,the change of temperature drop in the cooling zone and to control thecooling rate of the board material, for instance.

An apparatus suited for implementing the method comprises a chamberspace 2 including a first compartment 3 and means 6, 7 for passing agaseous treatment agent into said first compartment, a secondcompartment 4 and means 8, 9 for forming a vacuum into said secondcompartment of the chamber space, and further means 5, 16 for supportingthe board-like material in the chamber space, whereby the board-likematerial 1 under treatment itself forms at least a portion of the wallseparating the first compartment from the second compartment of saidchamber space. The apparatus is further characterized in that it isequipped with sensor elements 12, 13, 14, 15 for monitoring the statusof the material 1 being treated and/or of the gaseous treatment agent,that the apparatus is controlled as required on the basis of sensorelement output signals and that the apparatus includes means forcontrolling the state parameters of the gaseous treatment gas includingits temperature, moisture content and/or composition.

Accordingly, the apparatus needs means for conveying the board materialwithin the treatment zone. Such a means may be, e.g., a roller conveyor5 similar to the one shown in FIGS. 2 and 3, or any other type ofconveyor permitting free passage of gas through its structure. Theconveyor 5 or its immediate vicinity is provided with sealing means 16adapted to seal against the surface of the board 1, whereby the boardmaterial can form a portion of the intercompartmental wall whichseparates the at least one first compartment 3 from the at least onesecond compartment 4 of the treatment zone.

Advantageously, the seal means 16 are adapted to form a sealingperimeter which is in intimate contact with the surface of the boardmaterial. Advantageously, the apparatus also includes a second sealmeans 17 adapted above the board material as shown in FIG. 2.Advantageously, the seal means 17 forms a sealing perimeter and islower-able onto the surface of the board material. The seal means 17serves to enclose the gaseous emissions evaporating from the top surfaceof the board material into a closed space, thus preventing the emissionsfrom escaping into the ambient air. Thence, the treatment zone isadvantageously designed into a closed construction, whereby thetreatment gas and the obnoxious emissions possibly evaporating from theboard are effectively collected and passed to further processing orincineration, for instance.

The apparatus may also be complemented with a heat-recovering means suchas a heat exchanger, whereby the heat transferred from the boardmaterial into the gas can be utilized in some other process such asheating of buildings, for instance.

To those versed in the art it is obvious that the invention is notlimited by the exemplifying embodiments described above, but rather, canbe varied within the scope and spirit of the appended claims.

What is claimed is:
 1. A method for treating a board-like material witha gaseous treatment agent, the method comprising the steps of: a)introducing the board-like material into at least one treatment zone; b)contacting at least one side of the board-like material with the gaseoustreatment agent in the at least one treatment zone; c) causing thegaseous treatment agent to pass through the thickness of the board-likematerial in the at least one treatment zone; and d) using the gaseoustreatment agent to effect a change in the temperature of the board-likematerial in the at least one treatment zone.
 2. The method as defined inclaim 1, wherein the gaseous treatment agent effects a heating of theboard-like material.
 3. The method as defined in claim 1, wherein thegaseous treatment agent effects a cooling of the board-like material. 4.The method as defined in claim 1, and further comprising the step ofmoving the board-like material through the at least one treatment zone.5. The method as defined in claim 4, wherein the board-like material ismoved continuously through the at least one treatment zone.
 6. Themethod as defined in claim 4, wherein the board-like material is movedcyclically through the at least one treatment zone.
 7. The method asdefined in claim 1, wherein the board-like material is introduced into aplurality of treatment zones, and wherein: in at least one of theplurality of treatment zones, the treatment agent contacts a first sideof the board-like material and passes through the thickness of theboard-like material in a direction from the first side to a second sideof the board-like material; and in a treatment zone following the atleast one of the plurality of treatment zones, the treatment agentcontacts a first side of the board-like material and passes through thethickness of the board-like material in a direction from the second sideto the first side of the board-like material.
 8. The method as definedin claim 7, and further comprising the step of moving the board-likematerial through the plurality of treatment zones.
 9. The method asdefined in claim 8, wherein the board-like material is movedcontinuously through the plurality of treatment zones.
 10. The method asdefined in claim 8, wherein the board-like material is moved cyclicallythrough the plurality of treatment zones.
 11. The method as defined inclaim 1, and further comprising the following steps: collectingobnoxious emissions released by the board-like material in the at leastone treatment zone; and conducting the emissions away from the at leastone treatment zone to a facility where the emissions can be subjected tofurther processing.
 12. The method as defined in claim 1, and furthercomprising the step of conducting the gaseous treatment agent, followingits passage through the board-like material, to a heat exchanger, tothereby enable utilization of the residual heat of the gaseous treatmentagent after its employment in treating the board-like material.
 13. Themethod as defined in claim 1, and further comprising the step ofcontrolling the temperature of the gaseous treatment agent to therebyachieve favorable properties in the treated board-like material.
 14. Themethod as defined in claim 1, and further comprising the step ofcontrolling the moisture content of the gaseous treatment agent tothereby achieve favorable properties in the treated board-like material.15. The method as defined in claim 1, and further comprising the step ofcontrolling the composition of the gaseous treatment agent to therebyachieve favorable properties in the treated board-like material.